This invention relates to a cathode-preheated discharge tube lighting device such as a fluorescent lamp, and particularly to a high power factor and low-current lighting device.
For lighting a fluorescent lamp when the normal power source is 100 V, the voltage should be increased. Therefore, a conventional voltage multiplying rectifier, as shown in FIG. 1, is used as power supply input. The voltage multiplying rectifier comprises condensers EC.sub.1, EC.sub.2 and diodes D.sub.1, D.sub.2.
With this conventional voltage multiplying rectifier, however a phase difference between the voltage and current of the normal power source is produced by the capacitors EC.sub.1, EC.sub.2 in the process of rectification, thereby lowering the power factor by 60% and less. Accordingly, compensation of the phase difference is required. For this compensation, a phase equalizer comprising a low-frequency coil L.sub.1 and a condenser CO should be installed in the power source. However, the low-frequency coil L.sub.1 has disadvantages, in that it produces hum due to magnetic field resonance, and tend to overheat so that a great loss of power is caused.